JP2005177602A - Method of mixing flocculant, mixing vessel and method and apparatus for treating rain-water-including sewage using the mixing method and vessel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of mixing a flocculant and a mixing vessel which have ease of maintenance and permit uniform mixture without occurrence of a shunting flow and a method and an apparatus for treating rain-water-including sewage. <P>SOLUTION: The vessel has a turning flowing passage, an inlet for water 1 to be treated and a means of adding an inorganic flocculant 3 at the inlet portion of the passage, and a means of adding an organic polymer flocculant in the middle portion of the passage. The passage has means 4 and 7 setting the average flow rate of the to-be-treated water to be 0.18 m/s or higher for 3 s just after the addition of a flocculant and means 5 and 8 adjusting the average flow rate of the to-be-treated water to between 0.03 m/s and 0.18 m/s. The means setting the average flow rate to be 0.18 m/s or higher operates by making the cross-section of the passage or putting a baffle or an orifice plate in the passage. A solid-liquid separator is connected with the vessel to form an apparatus for treating rain-water-including sewage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to the treatment of sewage mixed with rainwater, and in particular, a method and a mixing tank for mixing a flocculant into sewage in a rainy day of a combined sewer in a sewage treatment plant, a pumping station, etc. The present invention relates to a method and apparatus for treating sewage mixed with rainwater.

Of the methods for separating suspended substances (hereinafter referred to as SS) contained in the water to be treated, the coagulation separation treatment is performed by adding a flocculant to the water to be treated to aggregate SS, followed by sedimentation separation and filtration. It is the processing method which isolate | separates or floats, and is called the coagulation precipitation process, the coagulation filtration process, and the coagulation flotation process, respectively. An important operation in these treatments is a mixing operation of an inorganic flocculant, and when an organic polymer flocculant is used, an operation of mixing an organic polymer flocculant is also important.
When an iron salt or aluminum salt is used as the inorganic flocculant, the reaction rate at which iron ions or aluminum ions form hydroxides in the water to be treated is high. For this reason, in order to effectively perform aggregation, it is necessary to diffuse the flocculant rapidly and uniformly in the water to be treated before the hydroxide is formed. Furthermore, after forming the hydroxide, it is necessary to perform uniform mixing in order to increase the opportunities for association and coalescence of the hydroxides and promote the formation of micro flocs.

On the other hand, in the mixing of the polymer flocculant, since the viscosity of the flocculant solution is high, the flocculant is uniformly diffused in the water to be treated, and at the same time, the flocculant and the micro floc are associated and coalesced. It is necessary to stir and mix rapidly. Further, in order to promote the growth of flocs by associating and combining the micro flocs, it is necessary to perform uniform mixing.
In the treatment of water containing sewage, the mixing operation of the flocculant is important for the same reason. When mixing is performed by mechanical stirring, the maintenance and management are complicated, such as the hair contained in the sewage wraps around the stirrer impeller and the mechanical operating unit may be broken. Moreover, a short circuit flow may occur and a cohesion failure may occur. On the other hand, the bypass mixing is applied to the formation of micro flocs after the inorganic flocculant is uniformly diffused, but because of the large head loss, mixing for the purpose of diffusion after addition of the inorganic flocculant or It is not applied to the mixing of polymer flocculants.
“Water Treatment Management Handbook” (Water Treatment Management Handbook Editorial Committee, 1998) p. 128-129 “Water Supply Facility Design Guidelines” (Japan Waterworks Association, 2000) p. 186-190

  The present invention solves the above-mentioned problems of the prior art, facilitates maintenance management in the sewage agglomeration treatment containing rainwater, effectively uses the site, performs uniform mixing without causing short-circuit flow, and floc It is an object of the present invention to provide a coagulant mixing method, a mixing tank, and a rainwater-mixed sewage treatment method and apparatus using the coagulant that can promote the growth of water and obtain clear treated water.

In order to solve the above-mentioned problems, the present invention provides a method for mixing a flocculant in which an organic flocculant is added and mixed after adding an inorganic flocculant to water to be treated by a bypass flow path. Mixing of each flocculant by the flow type flow path is carried out by setting the flow rate for a certain time immediately after the addition of each flocculant to be higher than the subsequent flow rate so that the flocculant is sufficiently contained in the treated water within the certain time. This is a method for mixing a flocculant characterized by diffusing into a solid.
In the flocculant mixing method, the flocculant is mixed by the bypass flow channel at an average flow rate of water to be treated of 0.18 m / sec or more for at least 3 seconds immediately after the addition of the flocculant, Thereafter, the coagulant mixing method is characterized in that the average flow rate of the water to be treated is 0.03 m / second or more and less than 0.18 / second.
Moreover, in this invention, it is set as the processing method of the rainwater mixed sewage which solid-liquid-separates, after adding and mixing the flocculant to the rainwater mixed sewage by the mixing method of the said flocculant.

Furthermore, the present invention has a bypass flow path, and has an inlet for the water to be treated and a means for adding an inorganic flocculant at the inlet of the flow path, and an organic coagulant at the middle of the flow path. In the flocculant mixing tank having the addition means of the system polymer flocculant, the bypass flow path has means for increasing the flow rate for a certain time immediately after the addition of the respective flocculants to be higher than the subsequent flow rate. This is a characteristic flocculant mixing tank.
In the flocculant mixing tank, the means for increasing the flow rate for a certain time immediately after the addition to the subsequent flow rate is to narrow the cross-sectional area of the flow channel or install a baffle plate or an orifice plate in the flow channel. In addition, the bypass flow path includes a means for setting the average flow rate of the water to be treated to 0.18 m / second or more for at least 3 seconds immediately after the addition of each of the flocculants, and thereafter the water to be treated. It is good to have a means to adjust the average flow velocity of 0.03 m / sec or more to less than 0.18 / sec.
Moreover, in this invention, it is set as the processing apparatus of the rainwater mixed sewage which has the said flocculant mixing tank which makes rainwater mixed sewage to-be-processed water, and a means to solid-liquid-separate the mixed treated water from this mixing tank. .

  According to the present invention, in the coagulation treatment of water containing sewage, it is excellent in maintenance and management, can effectively use the site, can perform uniform mixing without causing a short circuit flow, and increase the growth of flocs. Promote and provide clean treated water stably.

The present invention uses bypass mixing in mixing both the inorganic flocculant and the polymer flocculant into the water to be treated. Furthermore, the average flow rate of the water to be treated from immediately after the addition of the flocculant to after a certain time is increased, and the flocculant immediately after the addition is rapidly diffused. Thereafter, the average flow rate is reduced within a range effective for promoting the formation of micro flocs and the growth of flocs, and uniform mixing is performed.
In order to rapidly diffuse the flocculant into the water to be treated immediately after the addition of the flocculant, the average flow rate for 3 seconds at least immediately after the addition of the flocculant is set to 0.18 m / second or more. Thereafter, uniform mixing is performed to promote the formation of micro flocs in the inorganic flocculant mixture and the growth of flocs in the organic polymer flocculant mixture, and to keep the loss head low. 0.03 m / second or more and less than 0.18 m / second.

In the present invention, bypass mixing is adopted in both the mixing of the inorganic flocculant and the organic polymer flocculant, the water to be treated is introduced into the bypass mixing tank, the inorganic flocculant is added, and then the flocculant is added. At least 3 seconds after the addition of the agent, the average flow velocity for 3 seconds is set to 0.18 m / second or more, and the subsequent average flow velocity is set to 0.03 m / second or more and less than 0.18 m / second. Thereafter, an organic polymer flocculant is added, and the average flow velocity for at least 3 seconds is set to 0.18 m / second or more immediately after the addition of the flocculant, and the average flow velocity after that is set to 0. 03 m / sec or more and less than 0.18 m / sec.
In the present invention, as a means for increasing the flow rate for at least 3 seconds immediately after the addition of the flocculant, water flow agitation such as narrowing the flow path area, installing a baffle plate, or installing an orifice plate is used.

Next, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of a vertical detour-type mixing tank used in the present invention, which is an example in which a flow path cross-sectional area immediately after addition of a flocculant is narrowed.
The raw water 1 is introduced into the bypass type mixing tank 2, the inorganic flocculant 3 is added at the inflow portion, and immediately after the addition, the flow path 4 and the flow path 5 are flowed in this order. The channel 4 has a smaller cross-sectional area than the channel 5, and the average flow velocity of the channel 4 is faster than that of the channel 5. Here, the flow path 4 has an average flow rate of 0.18 m / second or more and a residence time of 3 seconds or more, and the inorganic flocculant is rapidly diffused. The flow path 5 has an average flow velocity of 0.03 m / second or more and less than 0.18 m / second, and the formation of micro floc is promoted. After passing through the channel 5, the organic polymer flocculant 6 is added, and immediately after the addition, the channel 7 and the channel 8 are flowed in this order. The channel 7 has a smaller cross-sectional area than the channel 8, and the average flow velocity of the channel 7 is faster than that of the channel 8. Here, the flow path 7 has an average flow rate of 0.18 m / sec or more and a residence time of 3 seconds or more, and the organic polymer flocculant is rapidly diffused and the flocculant and the micro floc are associated and combined. Is called. The channel 8 has an average flow velocity of 0.03 m / sec or more and less than 0.18 m / sec, and the micro flocs are assembled and combined to promote floc growth. After passing through the flow path 8, the water containing the grown floc flows from the bypass mixing tank 2 into the solid-liquid separation tank.
In addition to reducing the cross-sectional area, the flow path 4 and the flow path 7 have an average flow velocity of 0.18 m / min by installing the baffle plate 9 shown in FIG. 4 or the orifice plate 10 shown in FIG. It can be more than a second.

Based on the agglomeration treatment method of the present invention, an example of treatment using the bypass mixing tank of FIG. 1 is shown below.
For comparison, an example according to a flow of mechanically stirring the flocculant of FIG. 2 as a conventional example and a flow of bypassing the flocculant of FIG. 3 is shown. In FIG. 3, the cross-sectional area of the bypass channel is made constant, and the flow rate after adding the flocculant is the same for the flow channel 4 and the subsequent flow channel 5, and the flow channel 7 and the subsequent flow channel 8. In FIG. 1 of the present invention, the cross-sectional area of the flow channel after the addition of the flocculant is narrowed so that the flow rate is faster than the latter half of the flow channel.
In FIG. 2, which is mechanical agitation, ferric chloride is added to and mixed with raw water 1 in an inorganic flocculant mixing tank 9, and then anionic polymer flocculant 6 in a polymer flocculant mixing tank 10. Add and mix. The water containing the formed floc flows from the polymer flocculant mixing tank 10 into the solid-liquid separation tank.
On the other hand, the flow path of the bypass-type mixing tank 2 in FIG. 3 is reciprocated up and down four times, and after adding ferric chloride 3 to the upstream portion of the first flow path 4, two reciprocal flow paths are stirred. Do. Thereafter, the anionic polymer flocculant 6 is added to the upstream portion of the fifth flow path 7 and two reciprocal flow paths are stirred. The water containing the formed floc flows into the solid-liquid separation tank from the bypass mixing tank 2.

  The flow path of the bypass mixing tank 2 of FIG. 1 according to the present invention reciprocates up and down four times, and after adding ferric chloride 3 to the upstream portion of the first flow path 4, the flow path is reciprocated twice. Stir. The channel cross-sectional area of the first channel 4 is smaller than that of the second, third, and fourth channels 5 so that the average flow velocity is 0.40 m / sec. Thereafter, the anionic polymer flocculant 6 is added to the upstream portion of the fifth flow path 7, and two reciprocal flow paths are stirred. The channel cross-sectional area of the fifth channel 7 is smaller than those of the sixth, seventh, and eighth channels 8 so that the average flow velocity is 0.40 m / sec. Compared to FIG. 3, the average flow velocity of the first flow path 4 and the fifth flow path 7 is increased so that the diffusion is performed immediately after the addition of the flocculant. On the other hand, the average flow velocity of the second, third, fourth flow path 5 and the sixth, seventh, eighth flow path 8 is slowed to form micro flocs after flocculant diffusion and to grow flocs.

Table 1 shows the processing conditions and processing results of the present invention and the conventional method. The raw water was sewage in the rain of a combined sewer, and was treated at 147 m ³ / hour in any flow. In any treatment, ferric chloride was added at 30 mg / L as an inorganic flocculant, and anionic flocculant was added at 1.5 mg / L as an organic polymer flocculant. The raw water SS is about 150 to 300 mg / L and is the same. The mixing time is 120 seconds from the addition of the inorganic flocculant to the addition of the polymer flocculant, and 130 seconds from the addition of the polymer flocculant to the outflow of the mixing tank. In FIG. 2, the residence time of the inorganic flocculant mixing tank 9 is 120 seconds, and in FIGS. 1 and 3, the total residence time of the first flow path 4 and the second, third, and fourth flow paths 5 is 120 seconds. In FIG. 2, the residence time of the polymer flocculant mixing tank 10 is 130 seconds, and in FIGS. 1 and 3, the total residence time of the fifth flow path 7 and the sixth, seventh and eighth flow paths 8 is 130 seconds. It is. In the case of FIG. 3, the average flow velocity of the flow path is 0.15 m / sec throughout. On the other hand, in the case of FIG. 1, the average flow velocity of the first flow path 4 and the fifth flow path 7 is 0.40 m / second, the residence time is 11 seconds, and the average of the second, third, and fourth flow paths 5. The flow velocity is 0.12 m / second, the residence time is 109 seconds, the average flow velocity of the sixth, seventh and eighth flow paths 8 is 0.12 m / second, and the residence time is 119 seconds.

  In the mechanical stirring of the conventional method, the solid-liquid separation treated water SS is 20 to 58 mg / L, and the quality of the treated water is wide. By performing mechanical stirring, the ratio of the short-circuit flow is large, and the quality of the treated water becomes uneven. On the other hand, in the bypass-type stirring of the conventional method of FIG. 3, the solid-liquid separation treated water SS is 40 to 78 mg / L. Although short-circuit flow is prevented, the suspended substance remains in the treated water because the diffusion operation is insufficient immediately after the addition of the inorganic flocculant and immediately after the addition of the polymer flocculant. On the other hand, in the bypass stirring of the present invention, the solid-liquid separation treated water SS is 19 to 32 mg / L. A short-circuit flow is prevented, and the flocculant is diffused immediately and sufficiently immediately after addition of the flocculant, whereby clear treated water can be obtained.

The cross-sectional block diagram which shows an example of the bypass type mixing tank of this invention. Sectional block diagram of the mixing tank which mechanically stirs the conventional flocculant. The cross-sectional block diagram of the mixing tank which made the cross-sectional area of the conventional bypass waterway constant. The cross-sectional block diagram of the bypass type mixing tank which provided the baffle plate of this invention. The cross-sectional block diagram of the bypass type mixing tank which provided the orifice plate of this invention.

Explanation of symbols

  1: Raw water, 2: Detour type stirring tank, 3: Inorganic flocculant, 4, 5, 7, 8: Channel, 6: Organic polymer flocculant, 9: Baffle plate, 10: Orifice plate

Claims (7)

In the mixing method of the flocculant in which the organic polymer flocculant is added and mixed after adding and mixing the inorganic flocculant to the water to be treated by the bypass flow path, the mixing of each flocculant by the bypass flow path is performed by: Mixing of the flocculant characterized by sufficiently diffusing the flocculant into the water to be treated within the predetermined time by making the flow rate for a certain time immediately after the addition of each flocculant higher than the subsequent flow rate Method. In the mixing of each flocculant by the bypass channel, the average flow rate of the water to be treated is 0.18 m / sec or more for at least 3 seconds immediately after the addition of each flocculant, and thereafter the average flow rate of the water to be treated. The mixing method of the flocculant according to claim 1, wherein 0.03 m / sec or more and less than 0.18 m / sec. 3. A method for treating rainwater-mixed sewage, wherein the flocculant is added to the rainwater-mixed sewage by the mixing method according to claim 1 or 2, followed by solid-liquid separation. It has a bypass flow path, and has an inlet for the water to be treated and means for adding an inorganic flocculant at the inlet of the flow path, and an organic polymer flocculant in the middle of the flow path. In the flocculant mixing tank having addition means, the bypass flow path has means for increasing the flow rate for a predetermined time immediately after the addition of each of the flocculants to be higher than the subsequent flow rate. Tank. The means for making the flow rate for a certain time immediately after the addition faster than the subsequent flow rate narrows the cross-sectional area of the flow path, or installs a baffle plate or an orifice plate in the flow path. 4. The flocculant mixing tank according to 4. The bypass type flow path includes means for setting the average flow rate of the water to be treated to 0.18 m / second or more for at least 3 seconds immediately after the addition of the respective flocculants, and thereafter the average flow rate of the water to be treated is 0. The flocculant mixing tank according to claim 4, further comprising a means for adjusting to 0.03 m / second or more and less than 0.18 m / second. 7. A flocculated sewage comprising the flocculant mixing tank according to claim 4, 5 or 6, wherein the rainwater mixed sewage is treated water, and means for solid-liquid separation of the mixed treated water from the mixing tank. Processing equipment.

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